In image formation apparatuses, attempts have been made to reduce a startup period. It is necessary to supply a lot of electric power to a fixing device to achieve the reduction of a startup period successfully. However, the maximum suppliable electric power is generally limited in commercially available AC power supplies. Hence, in the related art image forming apparatuses, a capacitor or a rechargeable battery is provided with the image forming apparatus to temporarily supply high power from the rechargeable battery and the commercially available AC power supply to the fixing device simultaneously. This made it possible to reduce a warmup time of the fixing device, which results in the reduction in the startup period of the image forming apparatus.
However, in this related art method, it is necessary to control the electric power supply to the fixing device in accordance with a power control status of the power supplied to loads other than the fixing device in order not to allow electric power supply from the commercially available AC power supply to exceed the maximum electric power (the limit value). Thus, it is necessary to provide some unit for monitoring the power supply status of the power supplied to the loads other than the fixing device.
For example, Patent Document 1 (Japanese Laid-open Patent Publication No. 2005-221677) discloses an image forming apparatus provided with an electric power supply device capable of controlling electric power supplied to a fixing device to shorten the warmup time. In this technology, the electric power supply device is capable of restricting the electric power supplied from the commercially available power supply to a predetermined limit level. The electric power supply device of this image forming apparatus includes an electric power supply circuit to output electric power by reducing an alternating current voltage of the commercially available power supply to a predetermined direct current voltage. Hence, driving loads other than a heater of the fixing device may receive electric power from the commercially available power supply and/or a rechargeable battery. The power supply from the commercially available power supply and the rechargeable battery serving as the power supply to the driving loads when printing are such that the electric power supply from the commercially available power supply to the fixing device is restricted to the limit level based on the above-described control result.
However, the power supply status of the power supplied to the loads other than the fixing device is also required in this image forming apparatus in order to control the electric power from the commercially available power supply to the limit level.
Meanwhile, there are widely known in the art electric power supply devices that feed electric power to apparatuses by switching a main power supply and an auxiliary power. For example, Patent Document 2 (Japanese Laid-open Patent Publication No. 2007-209149) discloses an electric power supply device that includes a first power supply configured to output a constant voltage using electric power supplied from outside as an input source, and a second power supply using a rechargeable device and electric power of the rechargeable device as an input source so as to simultaneously supply electric power from the first power supply and electric power from the second power supply.
In the related art electric power supply device disclosed in Patent Document 2, the output of the second power supply is controlled based on the output current value of the first power supply. That is, the output current value of the first power supply is detected first, and electric power is supplied from the second power supply such that the detected output current value is a certain upper limit current value or less. In this manner, the rechargeable device may supply part of the electric power used by a constant voltage load. A fixing power supply of the electric power supply device uses an AC power source supplied from outside as an input source to supply AC power to cause the fixing heater to be conductive via fixing power instruction signals, which causes the fixing heater to generate heat.
It is generally known in the art that the maximum value of the electric power to heat the fixing heater exceeds electric power used by the constant voltage load. For example, the electric power used by the constant voltage load is approximately 600 W, and the maximum electric power for heating the fixing heater is set at 900 W. On the other hand, the above related art electric power supply device uses the AC power supply supplied from outside as an input source of the fixing power supply. Thus, the electric power supply device may fail to level the fixing power supply that consumes the electric power greater than the constant voltage load.
Further, the related art electric power supply device may cover the electric power for the constant voltage load with the electric power from the rechargeable battery alone; however, the fixing power supply uses the externally supplied AC power supply as the input source. Hence, all the electric power will not be covered by the electric power supplied from the rechargeable battery. Hence, the related art electric power supply device may fail to serve as a backup function when the external power supply is cut off such as during an electrical outage.